Russia's defense ministry said on Wednesday it had proof that Turkish President Tayyip Erdogan and his family were benefiting from the illegal smuggling of oil from Islamic State-held territory in Syria and Iraq.

Moscow and Ankara have been locked in a war of words since last week when a Turkish air force jet shot down a Russian warplane near the Syrian-Turkish border, the most serious incident between Russia and a NATO state in half a century.

Erdogan responded by saying no one had the right to "slander" Turkey by accusing it of buying oil from Islamic State, and that he would stand down if such allegations were proven to be true. But speaking during a visit to Qatar, he also said he did not want relations with Moscow to worsen further.